As a conventional overcurrent tripping device, for example, a configuration shown in FIG. 16 is known. In FIG. 16, when overcurrent flows through a conductor 101 penetrating through the center of the overcurrent tripping device, a magnetic flux is generated in a fixed core 102, to form a magnetic circuit, and a movable core 103 is attracted upward, whereby a shaft 104 fixed to the movable core 103 is moved upward. By the shaft 104 being moved upward, the retention state of a retention latch for a movable contact of a circuit breaker is released, whereby the circuit breaker shifts to an opened state (see, for example, Patent Document 1).